Terpenes are a naturally occurring class of hydrocarbons that are derived biosynthetically from isoprene (C5H8) units. Mono-terpenes consist of two isoprene units and have a molecular formula of C10H16. Mono-terpenes are non-oxygen containing bio-derived hydrocarbons that have appropriate volatility for consideration for use in gasoline.
Pinenes are bicyclic mono-terpenes, consisting of two isoprene units and have a molecular formula of C10H16. Turpentine is a mixture of various terpenes, including pinene, and is primarily derived from living trees (as gum turpentine) or as a by-product of the wood and paper pulp industry (as crude sulphate turpentine or CST).
The use of terpenes, and in particular pinenes, in fuel compositions is known for example, U.S. Pat. No. 1,405,809 discloses liquid fuel compositions which contain a terpene; in particular disclosing pine oil as a source of pinene.
U.S. Pat. No. 4,131,434 discloses in Table C an example of an additive formulation for a gasoline composition which contains a number of components, one of which is a terpene component. The additive formulation is tested in gasoline formulations for a range of properties, of which copper corrosion is one. No significant effect on copper corrosion is noted. The concentration of terpene component, specified as bicyclic compounds C10H16 pinene, in each gasoline composition tested is 0.018% vol.
It has been observed that the use of terpenes, in particular the use of terpene compositions comprising pinene in sufficient amounts, in gasoline compositions can give rise to various problems which it would be desirable to overcome.
In particular, it has been observed that the use of terpene compositions comprising pinene in a gasoline composition can cause an unacceptably high level of metal pick-up, i.e. the tendency to pick up metals (or leach metals) during transportation and storage in the supply and distribution system and also in vehicles fueled with the fuel. This unacceptably high level of metal pick-up may potentially lead to problems in the engine and the supply chain, for example the leached metals may lead to problems in terms of fouling of certain components.
Furthermore, steel corrosion caused by gasoline in engines and during the transportation of gasoline is undesirable and may also lead to problems in engines and the supply chain.